In a photomechanical process where a continuous tones densities of an original are converted respectively into the group consisting of the halftone dots having the areas proportional to the density, a silver halide photographic light sensitive material having a high contrast photographic characteristic is generally used.
For providing a high contrast characteristic to an image, a prefered photographic light sensitive material has been prepared in such a manner as described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP OPI Publication) No. 56-106244/1981 and U.S. Pat. No. 4,686,167; in which a compound such as hydrazine is contained as the so-called nucleating agent in a silver halide photographic light sensitive material and silver halide grains capable of effectively displaying the contrast-increasing characteristic of the compound are further used or other photographic additives are suitably used in combination. The silver halide photographic light sensitive materials such as those mentioned above are apparently proved to be stable as a light sensitive material and a high contrast photographic image can be obtained even when they are processed with a rapid processable developer.
However, the system applied with such a hydrazine compound as mentioned above has the disadvantage that a light sensitive material is to be developed generally at a high pH value, and a development has conventionally been made at a pH value of not lower than 11.5. Such a high alkaline developer as mentioned above is not suitable for a prolonged term preservation, because it is liable to an air oxidation and a development characteristic variation. Is is also unprefered from the viewpoints of the corrosion of developing equipments, the safety problems of operations and the environmental problems of waste liquids.
In regard to the avoidance of the problems of the high alkaline developers, European Patent Nos. 253,665, 333,435, 345,025 and 356,898, U.S. Pat. Nos. 4,988,604, 4,994,365 and 5,041,355 and JP OPI Publication Nos. 63-223744/1988, 63-234244/1988, 63-234245/1988, 63-234426/1988 and 2-77057/1990 disclose the silver halide photographic light sensitive materials each capable of obtaining a high contrast photographic image when making use of a developer having a pH, for example, not higher than 11.2. However, the contrast-increasing activity of the contrast-increasing agent applicable to the above-mentioned light sensitive materials have had such a disadvantage that an excellent halftone dot quality and a desirable black dot level (that is, a sand-like or pinhole-like fog produced in an unexposed area) cannot stably be obtained, because the pH of the developer is seriously varied when the pH of not higher than 11.2 is varied and the gamma and speed are liable to be varied when the pH is varied by the processing exhaustion or air oxidation of the developer.
It has therefore been demanded for a silver halide photographic light sensitive material capable of obtaining a sufficiently high contrast even when making use of a low pH developer and providing the stable photographic characteristics even when the pH is varied.
On the other hand, as one of the methods for forming a positive image with the use of a direct positive type silver halide photographic light sensitive material, there has been known a method for forming a positive image in which an unfogged internal latent image type silver halide emulsion is used and a surface development is carried out, after an exposure to light, in the presence of a foggant.
In the above-mentioned technical field, various techniques have been known so far. For example, these techniques include, typically, those described in U.S. Pat. Nos. 2,592,250, 2,456,957, 2,497,875 and 2,588,982, British Patent No. 1,151,363, JP Examined Publication No. 43-29405/1968, JP OPI Publication Nos. 47-9434/1972, 47-9677/1972, 47-32813/1972, 47-32814/1972, 48-9727/1973 and 48-9717/1973, U.S. Pat. Nos. 3,761,266 and 3,496,577 and JP OPI Publication Nos. 50-8524/1975 and 50-38525/1975.
As for the useful foggants, hydrazine compounds have been known.
For example, foggants applicable thereto include hydrazine compounds given in U.S. Pat. Nos. 2,563,758 and 2,588,982, naphthyl hydrazine sulfonic acid given in U.S. Pat. No. 2,064,700, and sulfomethyl hydrazines given in British Patent No. 1,403,018. Further, JP Examined Publication No. 41-17184/1966 describes that a color positive image is obtained by making use of hydrazide or a hydrazone compound.
However, when making use of the above-given compounds, the induction period before starting a development is longer than in the development of an ordinary latent image forming silver. Therefore, the development turns out to be considerably delayed.
When the conventional techniques are applied to a multilayered color photographic light sensitive material, these techniques have had such a problem that the characteristics are liable to cause an ununiformity between the layers and the resultant maximum density becomes lower.
For obtaining an excellent result while keeping a desirable fogging function, a development has been carried out at a high pH of not lower than 12. However, this type of developments have not desirable at all, because the deterioration of a developing agent is seriously accelerated and the physical property of layers of a photographic light sensitive material is deteriorated.
As for the direct-positive type silver halide photographic light sensitive materials, it has been demanded to provide a light sensitive material containing an advantageous foggant improved in the above-mentioned problems.